Volume 11, Issue 21, Pages 1695-1699 (October 2001) Cell cycle controlling the silencing and functioning of mammalian activators  Alan C. Mullen, Anne S. Hutchins, Alejandro V. Villarino, Hubert W. Lee, Frances A. High, Nezih Cereb, Soo Y. Yang, Xianxin Hua, Steven L. Reiner  Current Biology  Volume 11, Issue 21, Pages 1695-1699 (October 2001) DOI: 10.1016/S0960-9822(01)00533-4

Figure 1 Helper T cells as a model system for terminal differentiation. (a) Schematic of established and hypothetical regulation of gene expression. Naı̈ve (progenitor) cells, which have not undergone chromatin remodeling of IFN-γ or IL-4 loci [14, 22], may rapidly express T-bet and Gata-3, activators of the TH1 and TH2 fate, respectively. Committed TH1 (blue) and TH2 (red) cells have undergone chromatin remodeling of IFN-γ and IL-4 loci, respectively, mediated by T-bet [3] and Gata-3 [5]. Differentiation also involves heritable induction of T-bet or Gata-3, along with heritable silencing of the opposing activator [2, 4]. Experimental TH1 conditions inhibit development of TH2 fate because IL-12 favors growth of TH1 cells [3] and suppresses transcription of Gata-3 [7]. Experimental TH2 conditions inhibit TH1 fate because IL-4 favors growth of TH2 cells [6] and suppresses transcription of T-bet [3]. The present study tests the hypotheses (“?”) that S phase of the cell cycle plays a role in both (1) heritable silencing of activator loci and (2) the ability of activators to mediate heritable induction of signature cytokine loci. (b) T-bet (top) and Gata-3 (middle) mRNA levels were determined by RT-PCR in terminally differentiated TH1 and TH2 clones. Competitive amplification of HPRT was performed with an internal standard (bottom panel, upper band). (c) Naı̈ve cells were stimulated in experimental TH1 (left) or TH2 (right) conditions for 3 days. (d) Naı̈ve cells were stimulated in the presence of both anti-IL-4 and anti-IL-12 antibodies for 2 days in the absence (−) or presence (+) of G1 arrest, using mimosine throughout the article. (e,f) Cells were stimulated in TH1 conditions or TH2 conditions for 3 days in the absence (−) or presence (+) of mimosine. (g)Stat6−/− (left) or Stat4−/− (right) cells were stimulated for 24 hr in TH1 or TH2 conditions prior to infection with bicistronic Gata-3- or T-bet-GFP retrovirus (RV). After 2 more days, GFP and cytokine expression were determined by flow cytometry. Percentages above each column indicate frequency of untransduced (left portion) and transduced (right portion) cells expressing the indicated cytokine (y axis). (h) Cells were stimulated for 3 days in TH1 conditions with (right) or without (left) G1 arrest. Cells were then washed (Release) and re-stimulated in TH2 conditions for 4 days, in the absence of cell cycle inhibitors. Percentage of IL-4-positive cells is indicated. (i) Cells were treated as in (h), except initial stimulation was in TH2 conditions and cells were then released into TH1 conditions Current Biology 2001 11, 1695-1699DOI: (10.1016/S0960-9822(01)00533-4)

Figure 2 Cell division regulating repression of the activators Gata-3 and T-bet. (a) Cells were labeled with CFSE to resolve cell divisions (see Supplementary material) and stimulated in TH1 (left) or TH2 conditions (right). After 4 days, asynchronously dividing CD4+ cells were sorted by division number and mRNA levels among individual cell divisions were determined by RT-PCR for Gata-3 (TH1 conditions, left) and T-bet (TH2 conditions, right). (b) CFSE-labeled cells were stimulated and sorted as described in (a). Individual divisions were then washed extensively. Cells initially stimulated in TH1 conditions were restimulated in TH2 conditions plus anti-IFN-γ antibody (10 μg/ml), while cells initially stimulated in TH2 conditions were restimulated in TH1 conditions. After 4–5 days, cells switched into TH2 conditions were analyzed for IL-4 expression (three separate experiments) and cells switched into TH1 conditions were analyzed for IFN-γ expression (six separate experiments) by flow cytometry (see Supplementary material for sample data). The initial cell division number yielding the highest frequency of cytokine expression after switching was set at 100% (maximum), and the frequencies obtained from the other initial cell divisions were expressed as percentages of the maximum (% Max). In some experiments, divisions 0 and 1 were combined to obtain sufficient cell numbers Current Biology 2001 11, 1695-1699DOI: (10.1016/S0960-9822(01)00533-4)

Figure 3 Terminal TH commitment and silencing of activators during passage through S phase of the cell cycle. (a) Cells were stimulated in TH1 (left) or TH2 (right) conditions and simultaneously arrested either in S phase, using hydroxyurea (HU), or G2/M, using nocodazole (Noc). After 3 days, cells were washed (Release) and restimulated in the opposite conditions for 4 more days, in the absence of all cell cycle inhibitors. Cells were then analyzed for expression of CD4 (x axis) and either IL-4 or IFN-γ (y axes) by flow cytometry. (b) Cells were stimulated for 3 days in rIL-4 plus anti-IL-12 antibody and either allowed to proliferate (far left lane) or arrested at the indicated stages of the cell cycle using mimosine (Mim), hydroxyurea (HU), aphidicolin (Aph), nocodazole (Noc), or taxol (Tax). Levels of T-bet (top) and HPRT (bottom) mRNA were determined by RT-PCR. (c) Cells were stimulated for 3 days in anti-IL-4 and anti-IL-12 antibodies, prior to RT-PCR as in (b). Human rTGFβ (200 pM) and cell cycle inhibitors were used where indicated Current Biology 2001 11, 1695-1699DOI: (10.1016/S0960-9822(01)00533-4)

Figure 4 Activators of TH differentiation functioning in a cell cycle-dependent manner. (a)Stat4−/− cells were stimulated in the presence of rIL-4 for 24 hr prior to infection with T-bet- (top row) or control- (bottom row) GFP retrovirus (RV) and continued culture in rIL-4. 24 hr after retroviral infection, some cells were treated with mimosine (Mim) or hydroxyurea (HU), as indicated. All groups of cells were analyzed for GFP (x axis) and IFN-γ (y axis) expression 48 hr after retroviral infection. Frequency of IFN-γ-expressing cells in the untransduced (GFP-negative, left) and transduced (GFP-positive, right) populations is indicated above each column of cells. (b) Cells were stimulated for 3 days with no drug addition or in the presence of mimosine, sodium butyrate, or both, prior to analysis of IFN-γ (x axis) and IL-4 (y axis) expression. Percentages of cytokine-expressing cells are indicated. In both (a) and (b), only CD4+ gated events are displayed Current Biology 2001 11, 1695-1699DOI: (10.1016/S0960-9822(01)00533-4)